Carbon-carbon and/or ceramic matrix composite disks may be used as brake rotors and/or stators in automotive and aircraft brake systems. During the manufacture of these discs, non-woven fiber preforms may be placed in a furnace and subjected to multiple CVI/CVD process cycles. During these processes, multiconstituent hydrocarbons and/or other precursor process gases are deposited in the body of the preforms as pyrocarbon or other ceramic matrices. This processing is referred to as “densification” and results in an increase in the density of the preform with each process cycle. The process will be referred to as CVD. Before the first CVD process cycle, for example, the preforms may have a density of about 0.5 g/cc.
Normally, CVD processes are carried out on multiple composite preforms that have been arranged in stacks in a CVD furnace. The composite preform are generally annular or ring shaped and must be spaced from adjacent preforms to allow gases to flow around and into the preforms. One way of spacing the preforms is to manually place a number of separate spacers on a preform. Typically, about 8 to 12 spacers are used between layers in the stack. If a stack includes 10 preforms, for example, 72 to 84 separate spacers will have to be placed, which is a time-consuming process.
If too few spacers are used or if the spacers are not positioned properly, the spacers may leave indentations in the preforms that must be machined off. In some cases, the indentations are too deep to be removed completely, and preforms with such deep indentations must be discarded. Care must therefore be taken to position the spacers accurately so that the preforms above the spacers are properly supported and the weight of the higher preforms in the stack is evenly distributed across the surface of the lower preforms. It would be desirable to provide a method of densifying preforms that allowed for rapid and accurate placement of spacers.